1. Technical Field
The present invention relates to a spindle device which is provided with a spindle arranged to rotate freely about an axis, and attached with a tool and drive motors for rotating the spindle about the axis.
2. Description of the Related Art
Conventionally, as a spindle device, a spindle device disclosed in Japanese Examined Utility Model Application Publication No. 6-30325 is known, for example. The spindle device is configured by: a spindle which is arranged to rotate freely about an axis and of which distal end is attached with a tool; a support member which supports the spindle to rotate freely about the axis; a drive motor for rotating the spindle about the axis, the drive motor being configured by a rotor arranged to rotate freely on an outer circumferential surface on a rear end side of the spindle and a stator fixedly provided in the support member; a speed change mechanism for transmitting a rotational force of the drive motor directly or via a reduction gear to the spindle; and other components.
The speed change mechanism is formed of: an annular drive gear fixedly provided on an end surface at a distal end side of the spindle of the rotor; an annular clutch member which is provided on an outer circumferential surface of the spindle to face the drive gear and which is capable of moving freely in a spindle axial direction and rotating freely, together with the spindle; a speed change shaft which is disposed parallel to the spindle and which is arranged to move freely in an axial direction; a coupling member which couples the clutch member and the speed change shaft and which is connected to the clutch member and the speed change shaft such that the both components rotate freely about the axis; a drive cylinder for moving the speed change shaft in an axial direction; a first reduction gear and a second reduction gear which are fixedly provided to be kept apart by an interval in an axial direction of the speed change shaft; and a driven gear fixedly provided on the outer circumferential surface of the spindle to sandwich, together with the drive gear, the clutch member.
The drive gear is formed with teeth on both outer and inner circumferential surfaces. The clutch member is formed, on the outer circumferential surface on a side of the drive gear, with teeth which can be meshed with those formed on the inner circumferential surface of the drive gear. The first reduction gear is formed to be larger in diameter than the second reduction gear, and configured to be meshed with the teeth formed on the outer circumferential surface of the drive gear. The second reduction gear is configured to be meshed with the driven gear.
In the speed change mechanism, when the speed change shaft is moved in the axial direction by the drive cylinder, the speed change shaft, the clutch member, the coupling member, and the first and second reduction gears are integrally moved to a rear end side of the spindle. As a result, teeth of the clutch member and those on the inner circumferential surface of the drive gear are meshed, thereby resulting in a state where the teeth on the outer circumferential surface of the drive gear and the first reduction gear are not meshed and the second reduction gear and the driven gear are not meshed. Therefore, when the drive motor is then driven, a rotational force of the rotor is transmitted via the drive gear and the clutch member to the spindle, thereby rotating the spindle at high speed.
On the other hand, when the speed change shaft is moved in the axial direction by the drive cylinder, the speed change shaft, the clutch member, the coupling member, and the first and second reduction gears are integrally moved to a distal end side of the spindle. As a result, the teeth on the outer circumferential surface of the drive gear and the first reduction gear are meshed, and the second reduction gear and the driven gear are meshed, resulting in a state where the teeth of the clutch member and those on the inner circumferential surface of the drive gear are not meshed. Therefore, when the drive motor is then driven, the rotational force of the rotor is transmitted via the drive gear, the first reduction gear, the speed change shaft, the second reduction gear, and the driven gear to the spindle, thereby rotating the spindle at low speed.
In this way, according to the spindle device, since the speed change mechanism permits the spindle to rotate in a manner to switch between at high speed and at low speed, it is possible to correspond to both high speed and light duty cutting and low speed and heavy duty cutting.
However, in the conventional spindle device, the rotor of the drive motor and the spindle are in a state of being constantly coupled via the drive gear and the clutch member, or the drive gear, the first reduction gear, the speed change shaft, the second reduction gear, and the driven gear. Further, a drive force (rotational force of the rotor) of the drive motor is constantly transmitted to the spindle. Therefore, when a tool and a workpiece are interfered, for example, its shock is large and a serious accident may arise. Further, when the tool and the workpiece are interfered, or when lest perhaps the rotation of the spindle is stopped, an excessive load is applied to the drive motor, and as a result, the drive motor may be damaged.
Torque corresponding to the drive force of the drive motor is applied to the spindle, and thus, torque applied to the spindle becomes large. In this case, a force applied to a bearing for supporting the spindle to rotate freely becomes also large. When the force applied to the bearing is large, an operating life of the bearing is shortened and so on, which is a problem.
Further, the conventional spindle device is designed such that by moving the speed change shaft in the axial direction by the drive cylinder, the speed change shaft, the clutch member, the coupling member, and the first and second reduction gears are integrally moved in the axial direction of the spindle, thereby switching the spindle rotation between at high speed and at low speed. This results in another problem in that a structure becomes complicated and a device configuration becomes large.
Still further, a time required for increasing the rotational speed of the spindle to a previously set rotational speed or a time for stopping the rotation of the spindle depend on a performance or the like of the drive motor. If this time can be shortened, it is preferable.
In a spindle device configured such that a tool is attached directly or appropriately via a tool attaching member or the like to the spindle by means of a screw connection, if the tool or the tool attaching member is tightened to the spindle, it is difficult to loosen the tool or the tool attaching member when the tool is detached from the spindle, which results in a problem that detaching the tool is not easy.
The present invention has been achieved in view of the above-described circumstances, and an object thereof is to provide a spindle device configured to alleviate a shock caused as a result of a collision between a tool and a workpiece, to prevent an excessive load from being applied to a drive motor, to limit a maximum value of torque applied to the spindle to a certain value or less, and to be simple and compact. The object also is to provide a spindle device capable of shortening a time required for increasing a rotational speed of the spindle to a previously set rotational speed or stopping the rotation of the spindle, and capable of easily performing attaching and detaching the tool.